Magnetic resonance imaging method and device therefor

Abstract

A plurality of time-series NMR signal groups are obtained before and after administration of a contrast agent, on an individual image basis, for the same region of the object. One of the obtained NMR signal group obtained before the administration is defined as standard data, a plurality of subtracted NMR signal groups are produced by performing subtraction between the standard NMR signal group and each of the other NMR signal groups obtained after the administration. The subtracted NMR signal groups are subjected to weighted-addition or cumulative addition to obtain an MR angiographic image excellent in contrast throughout the image, in which processes through which an optimal concentration portion of the contrast agent moves are joined into a single image.

What is claimed is:  
     
       1. A magnetic resonance imaging method comprising the steps of applying a static magnetic field, gradient magnetic field and RF magnetic field to an object to be examined according to a predetermined pulse sequence, causing nuclear magnetic resonance (NMR) in nuclear spins within a given region of the object, measuring NMR signals caused by the NMR and displaying images produced using the measured signals, 
       wherein a plurality of time-series NMR signal groups are obtained, on an individual image basis, for the same region of the object, one of the obtained NMR signal group is defined as standard data, a plurality of subtracted NMR signal groups are produced by performing subtraction between the standard NMR signal group and each of the other NMR signal groups, the subtracted NMR signal groups are subjected to addition operation, a subtracted NMR signal group obtained by the addition operation is reconstructed and displayed as an image.  
     
     
       2. The magnetic resonance imaging method of  claim 1 , wherein the subtracted NMR signal groups to be added in the addition operation are weighted using weighting coefficients. 
     
     
       3. The magnetic resonance imaging method of  claim 2 , wherein the weighting coefficients are determined based on signal intensity of the subtracted NMR signal groups. 
     
     
       4. The magnetic resonance imaging method of  claim 2 , wherein weighting coefficients having different signs are used in the weighting operation. 
     
     
       5. The magnetic resonance imaging method of  claim 2 , wherein the weighting coefficients are so determined that arteries and veins are distinguishable. 
     
     
       6. The magnetic resonance imaging method of  claim 1 , wherein the method further comprises a step of administering a contrast agent to the object and the standard NMR signal group is measured before the contract agent arrives at a predetermined region of the object and the other NMR signal groups are measured while the contrast agent travels within the region. 
     
     
       7. The magnetic resonance imaging method of  claim 1 , wherein each of the NMR signal groups is capable of producing a two-dimensional image. 
     
     
       8. The magnetic resonance imaging method of  claim 1 , wherein each of the NMR signal groups is capable of producing a three-dimensional image. 
     
     
       9. The magnetic resonance imaging method of  claim 8 , wherein the three-dimensional image is projected in the desired direction to produce a two-dimensional image. 
     
     
       10. The magnetic resonance imaging method of  claim 1 , wherein the subtracted NMR signal groups are subjected to the cumulative addition. 
     
     
       11. The magnetic resonance imaging method of  claim 1 , wherein the subtraction of the NMR signal groups is performed on the measured complex signals. 
     
     
       12. A magnetic resonance imaging apparatus comprising means for applying a static magnetic field, gradient magnetic field and RF magnetic field by driving magnetic field generating units according to a predetermined pulse sequence, means for detecting NMR signals emitted from an object to be examined by the nuclear magnetic resonance, means for performing image reconstruction operation using the detected NMR signals, and means for displaying the obtained images, 
       wherein the apparatus further comprises means for generating a plurality of time-series NMR signal groups, on an individual image basis, for the same portion within the object by driving and controlling the magnetic field generating units, means for detecting and storing the plurality of NMR signal groups, means for producing a plurality of subtracted NMR signal groups by performing subtraction operation between a standard NMR signal group selected from the plurality of the NMR signal groups and the other NMR signal groups, means for performing addition operation on the plurality of subtracted NMR signal groups, and means for reconstructing an image using the result of the addition operation.  
     
     
       13. The magnetic resonance imaging apparatus of  claim 12 , wherein said means for performing addition operation performs the cumulative addition on the plurality of subtracted NMR signal groups. 
     
     
       14. The magnetic resonance imaging apparatus of  claim 12 , wherein the apparatus further comprises means for administering a contrast agent to the object and means for measuring the standard NMR signal group before administration of the contrast agent and measuring the other NMR signal groups successively while the contrast agent travels within the same portion of the object. 
     
     
       15. The magnetic resonance imaging apparatus of  claim 12 , wherein each of the NMR signal groups is capable of producing a two-dimensional image. 
     
     
       16. The magnetic resonance imaging apparatus of  claim 15 , wherein said means for performing addition operation performs weighting operation on the plurality of subtracted NMR signal groups using weighting coefficients. 
     
     
       17. The magnetic resonance imaging apparatus of  claim 16 , wherein weighting coefficients having different signs are used in the weighting operation. 
     
     
       18. The magnetic resonance imaging apparatus of  claim 12 , wherein each of the NMR signal groups is capable of producing a three-dimensional image. 
     
     
       19. The magnetic resonance imaging apparatus of  claim 18 , wherein the apparatus further comprises means for performing projection operation on the three-dimensional image. 
     
     
       20. The magnetic resonance imaging apparatus of  claim 12 , wherein said means for producing a plurality of subtracted NMR signal groups performs the subtraction operation on the measured complex signals. 
     
     
       21. A magnetic resonance imaging method comprising the steps of applying a static magnetic field, gradient magnetic field and RF magnetic field to an object to be examined according to a predetermined pulse sequence, causing nuclear magnetic resonance (NMR) in nuclear spins within a given region of the object, measuring NMR signals caused by the NMR and displaying images produced using the measured signals, 
       wherein a plurality of time-series NMR signal groups are obtained, on an individual image basis, for the same region of the object, one of the obtained NMR signal group is defined as standard data, a plurality of subtracted NMR signal groups are produced by performing subtraction between the standard NMR signal group and each of the other NMR signal groups, the subtracted NMR signal groups are reconstructed to produce images, and the reconstructed images are subjected to addition operation, and an image obtained by the addition operation is displayed.  
     
     
       22. The magnetic resonance imaging method of  claim 21 , wherein the subtracted NMR signal groups to be added in the addition operation are weighted using weighting coefficients. 
     
     
       23. The magnetic resonance imaging method of  claim 22 , wherein the weighting coefficients are determined based on signal intensity of the subtracted NMR signal groups. 
     
     
       24. The magnetic resonance imaging method of  claim 22 , wherein weighting coefficients having different signs are used in the weighting operation. 
     
     
       25. The magnetic resonance imaging method of  claim 22 , wherein the weighting coefficients are determined so that contrast difference between arteries and veins is enhanced. 
     
     
       26. The magnetic resonance imaging method of  claim 21 , further comprising a step of administering a contrast agent to the object and the standard NMR signal group is measured before the contract agent arrives at a predetermined region of the object and the other NMR signal groups are measured while the contrast agent travels within the region. 
     
     
       27. The magnetic resonance imaging method of  claim 21 , wherein each of the NMR signal groups is capable of producing a two-dimensional image. 
     
     
       28. The magnetic resonance imaging method of  claim 21 , wherein each of the NMR signal groups is capable of producing a three-dimensional image. 
     
     
       29. The magnetic resonance imaging method of  claim 28 , wherein the reconstructed images are projected in the desired direction to produce two-dimensional images and the two-dimensional images are subjected to addition operation. 
     
     
       30. The magnetic resonance imaging method of  claim 28 , wherein the reconstructed images are subjected to addition operation to produce a three-dimensional image and the three-dimensional image is projected in the desired direction to produce a tow-dimensional image. 
     
     
       31. The magnetic resonance imaging method of  claim 21 , wherein the subtracted NMR signal groups are subjected to the cumulative addition. 
     
     
       32. The magnetic resonance imaging method of  claim 21 , wherein the subtraction of the NMR signal groups is performed on the measured complex signals. 
     
     
       33. A magnetic resonance imaging apparatus comprising means for applying a static magnetic field, gradient magnetic field and RF magnetic field by driving magnetic field generating units according to a predetermined pulse sequence, means for detecting NMR signals emitted from an object to be examined by the nuclear magnetic resonance, means for performing image reconstruction operation using the detected NMR signals, and means for displaying the obtained images, 
       wherein the apparatus further comprises means for generating a plurality of time-series NMR signal groups, on an individual image basis, for the same portion within the object by driving and controlling the magnetic field generating units, means for detecting and storing the plurality NMR signal groups, means for producing a plurality of subtracted NMR signal groups by performing subtraction operation between a standard NMR signal group selected from the plurality of the NMR signals groups and the other NMR signal groups, means for reconstructing images using the subtracted NMR signal groups and means for performing addition operation on the reconstructed images.  
     
     
       34. The magnetic resonance imaging apparatus of  claim 33 , wherein said means for performing addition operation performs the cumulative addition on the plurality of subtracted NMR signal groups. 
     
     
       35. The magnetic resonance imaging apparatus of  claim 33 , wherein the apparatus further comprises means for administering a contrast agent to the object and mans for measuring the standard NMR signal group before administration of the contrast agent and measuring the other NMR signal groups successively while the contrast agent travels within the same portion of the object. 
     
     
       36. The magnetic resonance imaging apparatus of  claim 33 , wherein each of the NMR signal groups is capable of producing a two-dimensional image. 
     
     
       37. The magnetic resonance imaging apparatus of  claim 33 , wherein each of the NMR signal groups is capable of producing a three-dimensional image. 
     
     
       38. The magnetic resonance imaging apparatus of  claim 37 , wherein the apparatus further comprises means for performing projection operation on the three-dimensional image before the addition operation. 
     
     
       39. The magnetic resonance imaging apparatus of  claim 37 , wherein the apparatus further comprises means for performing projection operation on the three-dimensional image after the addition operation. 
     
     
       40. The magnetic resonance imaging apparatus of  claim 33 , wherein said means for producing a plurality of subtracted NMR signal groups performs the subtraction operation on the measured complex signals. 
     
     
       41. The magnetic resonance imaging apparatus of  claim 33 , wherein said means for performing addition operation performs weighting operation on the plurality of subtracted NMR signal groups using weighting coefficients. 
     
     
       42. The magnetic resonance imaging apparatus of  claim 33 , wherein weighting coefficients having different signs are used in the weighting operation.